How to remedy excessively long tempering time for H13 material?

Re-quenching and uniform tempering are the solutions for excessively long tempering times in H13 material. The material characteristics can be restored by precisely heating the material and reestablishing a homogeneous martensitic structure. The quantity of rework activities, however, needs to be tightly regulated.

1. Steps in the Corrective Process

Procedures

Important Points

Goals

Re-quenching

Heat to 1020–1050°C, then either air-cool or oil-cool.

Rebuild a smooth, consistent martensite structure

② Consistent tempering

Perform two cycles of tempering at 550–600°C for at least two hours each.

Release stress and precisely regulate hardness at 48–52 HRC.

③ Multi-point evaluation

Test three to five spots per part using a portable hardness tester with a range of less than two HRC.

Check for consistency and confirm the corrective effect.

Actual Case: After five hours of tempering, the hardness of an H13 mold core decreased to 46.8 HRC. The hardness recovered to 49.5 HRC after re-quenching + 580℃×2h×2 tempering cycles, satisfying the usage criteria.

 

2. Corrective Requirements and Risk Management

Remedial Conditions: Workpiece without deformation or cracking; Metallographic structure without network carbides or microcracks; Hardness < 48 HRC but no surface decarburization or oxidation.

Use cautiously or without taking corrective action since it has undergone more than two heat treatments, there is a high danger of grain coarsening, thick-walled parts have microcracks, and customers have stringent requirements on heat history traceability.

It is advised that samples be subjected to metallographic analysis prior to remediation in order to determine whether the microstructure is appropriate for rework.

 

3. Steps to Stop Time Limits from Recurring

Establish a time limit: 5 hours, or 100 mm of thickness, is the maximum amount of time that thick parts should be tempered;

Turn on process monitoring: To avoid human mistake, use a PID temperature control system with time recording;

Choose compliant service providers: For more standardized procedures, give priority to working with CQI-9 accredited heat treatment facilities (such Wuhan Heat Treatment Plant and Jingmo Technology).